1. Field of the Invention
Embodiments of the present invention relate generally to lithium-ion batteries, and more specifically, to a method of fabricating such batteries using thin-film deposition processes that form three-dimensional structures.
2. Description of the Related Art
Fast-charging, high-capacity energy storage devices, such as supercapacitors and lithium—(Li) ion batteries, are used in a growing number of applications, including portable electronics, medical, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supply (UPS). In modern rechargeable energy storage devices, the current collector is made of an electric conductor. Examples of materials for the positive current collector (the cathode) include aluminum, stainless steel, and nickel. Examples of materials for the negative current collector (the anode) include copper (Cu), stainless steel, and nickel (Ni). Such collectors can be in the form of a foil, a film, or a thin plate, having a thickness that generally ranges from about 6 to 50 μm.
The active electrode material in the positive electrode of a Li-ion battery is typically selected from lithium transition metal oxides, such as LiMn2O4, LiCoO2, and combinations of Ni or Li oxides and includes electroconductive particles, such as carbon or graphite, and binder material. Such positive electrode material is considered to be a lithium-intercalation compound, in which the quantity of conductive material is in the range from 0.1% to 15% by weight.
Graphite is usually used as the active electrode material of the negative electrode and can be in the form of a lithium-intercalation meso-carbon micro beads (MCMB) powder made up of MCMBs having a diameter of approximately 10 μm. The lithium-intercalation MCMB powder is dispersed in a polymeric binder matrix. The polymers for the binder matrix are made of thermoplastic polymers including polymers with rubber elasticity. The polymeric binder serves to bind together the MCMB material powders to preclude crack formation and prevent disintegration of the MCMB powder on the surface of the current collector. The quantity of polymeric binder is in the range of 2% to 30% by weight.
The separator of Li-ion batteries is typically made from microporous polyethylene and polyolefine, and is applied in a separate manufacturing step.
For most energy storage applications, the charge time and capacity of energy storage devices are important parameters. In addition, the size, weight, and/or expense of such energy storage devices can be significant limitations. The use of electroconductive particles and MCMB powders and their associated binder materials in energy storage devices has a number of drawbacks. Namely, such materials limit the minimum size of the electrodes constructed from such materials, produce unfavorable internal resistance in an energy storage device, and require complex and eclectic manufacturing methods.
Accordingly, there is a need in the art for faster charging, higher capacity energy storage devices that are smaller, lighter, and can be more cost effectively manufactured.